dt-bindings: iio: dac: Add adi,ltc2664.yaml

Add documentation for ltc2664.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Co-developed-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Kim Seer Paller <kimseer.paller@analog.com>
Link: https://patch.msgid.link/20240718051834.32270-5-kimseer.paller@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>